Summary of Work A. Thirty-four tumor specimens from small cell lung cancer patients were studied for myc family DNA amplification. None of the 11 tumor specimens obtained from untreated patients had DNA amplification of any of myc family. Six of 23 tumor specimens obtained from chemotherapy treated patients had DNA amplification of the myc family (4 N-myc, 2 L-myc) B. Twenty-six tumor specimens and normal tissues were obtained from different small cell lung cancer patient treated at the NCI-Navy Medical Oncology Branch. DNA was prepared, digested with appropriate restriction enclonucleases, and hybridized to 4 probes which detect restriction fragment length polymorphisms (RFLP) in DNA. Twenty-five were heterozygous for at least one allele. The DNA from tumors showed deletion of one of the heterozygous alleles in 23 of the 25 patients. One of the 2 exceptions was a patient with extrapulmonary small cell lung cancer. From these RFLP studies we concluded the deletion of 3p alleles is present and common in small cell lung cancer providing additional evidence for deletion of the short arm of chromosome 3 in small cell lung cancer.